This invention relates to improvements in and relating to an arrangement for precise and continuous measurement of yarn thickness and mass while the yarn is running by use of a static capacitance type sensor.
It is commonly known to use a static capacitance type sensor having a pair of opposing electrodes defining a gap passage for the yarn under measurement by and between these electrodes. In order to control the spinning conditions on location where at least several thousand yarns are being manufactured, each spinning unit must be provided with such a sensor. This kind of sensor must have outer dimensions which are as small as possible without sacrificing its precise operational performance.
According to our experimental study, future dyeing capability of the yarn can be estimated at the manufacture or winding or packaging stage of the process and in advance of the practical dyeing of the yarn, by precise and fine measurement of denier variations thereof taken along its whole length. For such purpose, the above mentioned kind of sensor must be utilized.
In order to realize a smaller possible sensor of the static capacitance type with superior operation performance, it is necessary to shorten the length of the electrode as much as possible when seen in the running direction of the yarn; ideally to a point. If the yarn denier measurement could be carried out continuously at a point or in the differential way so to speak, the measured result would be best. But, in practice, such measurement mode has only an ideal significance.
In order to precisely take out the electrical output from the statical capacitance sensor, a resonance circuit must have been coupled with the electrode pair due to the extremely small variations of the capacitance measured in correspondence to those of the yarn denier.
With use of the resonance circuit for an extended time period, appreciable variation in the temperature characteristic of each of the circuit components will be encountered, resulting in the corresponding shift of the resonance point. A usable time period of such a measuring arrangement having a static capacitance sensor and resonance circuit may be in the order of 2 - 3 minutes if the precise measurement of fine and smaller yarn denier variations are to be performed in a satisfactory manner. In order to avoid such adverse effect, the condenser capacitance of the sensor must have a reasonably large value, such as, preferably, 10 pF or so. The corresponding electrode length may be in the order of 10 cm.
If the impedance drop method is employed in place of the resonance system, the sensitivity will drop considerably by virtue of the nonemployment of the resonance amplification. In this case, therefore, the amplifier used for the amplification of output signal from the sensor must have a considerably large amplifying factor which results in a considerable rise in the amplifier cost.